Method and apparatus for measuring corrosion rates



Dec. 15, 1964 c. w. GERHARDT 3,161,042

METHOD AND APPARATUS FOR MEASURING CORROSION RATES Original Filed June9, 1955 INVENTOR. awn w. i/fW/FAW' 2 3' ||||||11|||1|||||l|ll|1|| BY 0m4: 04m EXPOSURE Z 7 a,

United States Patent Office 3,16 1,642 Patented Dec. 15., 1964 Theinvention described herein may be manufactured and used by or for theUnited States Government for governmental purposes withoutpayment to meif any royalty thereon.

This invention is a division of my copending application Serial Number54,553 filed September 7, 1960, now Patent No. 3,112,641 which, in turn,is a division of application Serial Number 514,408, filed June 9, 1955and matured into United States Patent Number 2,972,248. The

invention relates to an apparatus for measuring the corrosivity of .anatmosphere or environment or for measuring the corrodibility of aresilient member such as a spring and could also be used to measureerosive rates.

The conventional method to measure corrosivity of an environment or thecorrodibility of material is to prepare a test sample or samples, putthem in a corrosive environment and measure the loss in weight of thesamples after a fixed period of time. Such a method requires anextremely accurate balance and it has been necessary to run a largenumber of samples averaging results to make any reasonably accurateestimation of corrosiveness. There seem to be a number of factors thatinfluence the accuracy of this method including the original preparationof the samples and the handling and preparation of the samples afterexposure prior to weighing.

It is an object of this invention to provide an improved apparatus fortesting corrosion rates wherein a measurement is made indicative of thechange of strength of a resilient member with time as an indication ofcorrosion rate.

It is another object of this invention to provide an improved apparatusfor measuring the corrosivity of an environment or an atmosphere whereinsuch information is obtained from a measurement indicative of the changeof strength with time of the resilient member.

It is a further object of this invention to provide an improvedapparatus for measuring the corrosion rate of a resilient material suchas a spring wherein such information is obtained from a measurementindicative of the change of strength of the resilient member.

It is yet another object of this invention to provide an improved methodand apparatus for testing erosion rates wherein a measurement is madeindicative of the. change of strength of a resilient member with time asan indication of the erosion rate.

These and other objects of the invention will become apparent as thedetailed description of the invention proceeds.

The invention will be more clearly understood from the followingdetailed description of specific examples thereof read in conjunctionwith the accompanying drawing wherein:

FIGURE 1 is a sectional elevational view of one embodiment of myinvention;

FIGURE 1a is a partial elevational view of the scale and zero adjustmeans of the embodiment of FIGURE 1;

FIGURE 2 is an elevational view of another embodiment of my invention;and

FIGURE 3 is a typical graphical presentation of the data obtained froman embodiment of my invention such as is shown in FIGURE 1.

' FIGURE 1 shows a first embodiment of the apparatus of my invention. Aframe 11 having a peripheral notch 13 in the top surface thereof acts asa support for the apparatus. A helical spring 1-2 is positioned in notch13. Weight 14 having a peripheral notch 15 in the bottom surface thereofand an axial passage 16 therethrough is positioned on spring 12 to actas a compressive force on the spring. The spring is positioned in notch15 of the weight. For the purpose of indicating the change in positionof weight 14 a scale 17, which is L-shaped and has a bottom portion174:. as a part thereof, is attached by screws 18 or other suitablemeans to frame 11. This scale projects axially up through spring 12. andthrough passage 16 in weight 14. A zero adjust collar 19 having a setscrew 20 is positioned on scale 17. Collar 19 is a split ring cylinderas shown in FIGURE 1a. This arrangement facilitates the reading of thezero point.

Obviously the scale 17 need not be a part of the apparatus itself. Aseparate scale could be used to make the measurements. However, forconvenience and accuracy it is preferred'to use an attached scale. Alsothe zero adjust rncans (1 9 and 20) could be eliminated from theapparatus, but for convenience and accuracy it is preferred 'zero adjustcollar 19 is positioned with its bottom portion touching the top ofweight 14. A reading is then made of this zero position on the scale. Anumber of days or weeks or months are allowed to pass and a reading ismade of the scale distance between the zero adjust collar =19 and theweight 14. These readings are normally made at spaced intervals fromtime to time. Data obtained from these readings may be plotted in amanner similar to that shown in FIGURE 3. A curve somewhat similar tothat shown in :FIGURE 3 will be obtained. This curve is indicative ofthe corrosiveness of the particular environment or atmosphere in whichthe apparatus has been placed and of the corrodibility of spring 12.Obviously the apparatus may be used to test either the environment orthe spring. The spring must be made of material which will show ameasurable change in compressive strength with time in the test.Normally some sort of nonstainless steel would probably be used for thespring.

FIGURE 2 shows another embodiment of my invention which is really thesame embodiment as is described in FIGURE 1 except that the helicalspring is in tension rather than compression as in FIGURE 1. Thisembodiment is supported from an overhead support 21. Frame 22 isattached by screws 23 or other suitable means to support 21. A helicalspring 24 is rigidly attached to frame 22 by Welding, brazing or othersuitable means. Spring 24 could be attached to frame 22 by screwing thespring into a threaded channel (not shown) in frame 22. A weight 25 isrigidly attached to the lower end of spring 24. This weight may beattached to the spring in the same manner as the spring is attached tothe frame. Weight 25 has an axial channel 25a therethrough foraccommodating scale 26 which is rigidly attached to frame 22 by welding,brazing or other'suitable means. As shown, scale 26 projects axiallythrough spring 2-41 and weight 25.

The apparatus of FIGURE 2 would be used in a method similar to thatdescribed in which the apparatus of FIGURE 1 was used except that thereadings in this case would be taken from the bottom of weight 25 onscale26 and no zero adjust means would be used in this case. A readingwould be taken at zero exposure time of the apparatus and at spaced timeintervals during the exposure. A separate scale, i.e., not a part oftheapparatus, may be used for measurements but the attached scale ispreferred for convenience. In this case the change in tensile strengthrather than compressive strength of the spring would be indicated. It ispreferred though not absolutely necessary that all other parts exceptthe springs of the apparatus of both FIGURES 1 and 2 be made of anoncorrosive material for appearance sake, or these parts might becoated with some protective coating.

As has been previously mentioned FIGURE 3 shows a typical plot of datawhich might be obtained from the apparatus.

Although the invention has been described in terms of specifiedapparatus which is set forth in considerable detail, it should beunderstood that this is by way of illustration only and that theinvention is not necessarily limited thereto, since alternativeembodiments and operating techniques will become apparent to thoseskilled in the art in view of the disclosure. For example, the variousapparatus embodiments of the invention can be used in the determinationof erosive rates as well as corrosive rates, i.e., to determine theerosiveness of an environment or atmosphere or the erodibility of aresilient member. The resilient member would be made of suitableerodible material for measuring the erosiveness of an atmosphere orenvironment, and in many cases this material could be the same materialas would be used for corrosive rate measurements. The fact that aresilient member made of the same material can in many cases be used tomeasure both corrosive rates and erosive rates is fortunate sincesometimes an environment or atmosphere will have both corrosive anderosive properties. Accordingly, modifications are contemplated whichmay be made without departing from the spirit of the described inventionor of the scope of the appended claims.

What is claimed is:

1. A corrosion rate measuring apparatus comprising a circular framehaving a circumferential notch in the upper surface thereof, acorrodible helical spring positioned in said notch and supported by saidframe, said spring being made of such' material that it will losemeasurable resistance to compressive strength with time in a corrosiveenvironment, a cylindrical weight having a circumferential notch in thelower surface thereof and an axial opening therethrough, said weightbeing supported by said spring the upper end of which is positioned inthe notch of said weight, a scale attached to said frame, said scaleprojecting axially through said spring and said weight, and a zeroadjust means attached to said scale above said weight, said scale andweight cooperating to produce differing relative positions, over periodsof time, which are indicative of the corrosion rates for said periods oftime.

2. A corrosion rate measuring apparatus comprising a frame, a corrodiblehelical spring supported by and depending from said frame, said springbeing made of such material that it will lose measurable tensilestrength when placed in a corrosive environment, a weight having anaxial opening therethrough supported by said spring in such a fashionthat said spring is put in tensile stress by said weight, and a scalerigidly attached to said frame, said scale projecting axially throughsaid spring and said weight, said scale and Weight cooperating toproduce differing relative positions, over periods of time, which areindicative of the corrosion rates for said periods of time.

References Cited by the Examiner UNITED STATES PATENTS 2,049,644 8/36Essen 73-16l 2,164,453 7/39 Gaskins 73-l6l 2,568,596 9/51 Ruge 73161RICHARD C. QUEISSER, Primary Examiner.

1. A CORROSION RATE MEASURING APPARATUS COMPRISING A CIRCULAR FRAMEHAVING A CIRCUMFERENTIAL NOTCH IN THE UPPER SURFACE THEREOF, ACORRODIBLE HELICAL SPRING POSITIONED IN SAID NOTCH AND SUPPORTED BY SAIDFRAME, SAID SPRING BEING MADE OF SUCH MATERIAL THAT IT WILL LOSEMEASURABLE RESISTANCE TO COMPRESSIVE STRENGTH WITH TIME IN A CORROSIVEENVIRONMENT, A CYLINDRICAL WEIGHT HAVING A CIRCUMFERENTIAL NOTCH IN THELOWER SURFACE THEREOF AND AN AXIAL OPENING THERETHROUGH, SAID WEIGHTBEING SUPPORTED BY SAID SPRING THE UPPER END OF WHICH IS POSITIONED INTHE NOTCH OF SAID WEIGHT, A SCALE ATTACTED TO SAID FRAME,